Plastic containers are easy to form, can be inexpensively produced and have, therefore, been widely used in a variety of applications. Specifically, an olefin resin container of the shape of a bottle of which the inner wall surface is formed by using an olefin resin such as low-density polyethylene and which is formed by direct blow-forming, has been desirably used as a container for containing viscous slurry-like or paste-like contents such as ketchup and the like from such a standpoint that the content can be easily squeezed out.
Further, the bottles containing viscous contents are, in many cases, preserved in an inverted state to quickly discharge the contents or to use the contents to the last drop without leaving them in the bottle. It is, therefore, desired that when the bottle is inverted, the viscous content quickly falls down without adhering or staying on the inner wall surface of the bottle.
To satisfy such requirements, for example, a patent document 1 proposes a bottle of a multilayer structure of which the innermost layer is formed from an olefin resin having an MFR (melt flow rate) of not less than 10 g/10 min.
The innermost layer of this multilayer structure bottle has excellent wettability for the oily content. Therefore, if the bottle is inverted or is tilted, then the oily content such as mayonnaise or the like falls down spreading along the surface of the innermost layer and can be completely discharged without adhering or remaining on the inner wall surface of the bottle (on the surface of the innermost layer).
As for the bottles for containing viscous non-oily contents in which plant fibers are dispersed in water like ketchup, a patent document 2 and a patent document 3 are disclosing polyolefin resin bottles having an innermost layer which is blended with a saturated or unsaturated aliphatic amide as a lubricating agent.
The above patent documents 1 to 3 are all trying to improve slipping property of the plastic containers for the contents based on the chemical compositions of the thermoplastic resin compositions forming the inner surfaces of the containers, and are achieving improvements in the slipping property to some extent. However, limitation is imposed on improving the slipping property due to limitation on the kinds of the thermoplastic resins that are used and on the additives, and striking improvement has not been achieved yet.
Under the above circumstances, in recent years, study has been forwarded to improve slipping property from the physical point of view, too.
For instance, a patent document 4 is proposing a container in which fine hydrophobic oxide particles of an average primary particle size of 3 to 100 nm are adhered on the inner surface thereof.
Further, a patent document 5 is proposing a lid body forming on the surface thereof a water-repellent film of a structure in which fine oxide particles of an average particle size of 5 nm to 100 nm are dispersed and adhered on the surface of a resin film formed from resin particles of an average particle size of 1 μm to 20 μm.
Technologies proposed by the patent documents 4 and 5 are to produce water-repellent property (hydrophobic property) based on a finely rugged surface which is formed on a surface to which the content comes in contact. Namely, an air layer is formed in the voids present in the rugged surface in addition to utilizing the hydrophobic property of the material forming the rugged surface. The air layer repels water more than the material that forms the container and, as a result, the aqueous content is more restrained from adhering.
When the finely rugged surface is formed, adhesion of the aqueous content can be more restrained. With the content being in contact with the finely rugged surface at all times, however, water tends to be condensed very easily in the dents in the finely rugged surface; i.e., dents are filled with the condensed water. As a result, the slipping property decreases and, therefore, it becomes necessary to further improve the slipping property.